Impedance conversion circuit and integrated circuit including thereof

ABSTRACT

An impedance conversion circuit including: a first voltage-to-current converter and a second voltage-to-current converter supplied with differential input signal voltages; an inverting amplifier; and a third voltage-to-current converter for feedback; wherein a first resistance and a second resistance are connected in series with each other between an input terminal and an output terminal of the inverting amplifier, an output terminal of the first voltage-to-current converter is connected to the input terminal of the inverting amplifier, an output terminal of the second voltage-to-current converter is connected to a connection node of the first resistance and the second resistance, the output terminal of the inverting amplifier is connected to an input terminal of the third voltage-to-current converter, an output terminal of the third voltage-to-current converter is connected to an input terminal of the first voltage-to-current converter, and an impedance is connected between the connection node and a ground.

CROSS REFERENCES TO RELATED APPLICATIONS

The subject matter of application Ser. No. 11/441,689 is incorporatedherein by reference. The present invention is a continuation of U.S.application Ser. No. 11/441,689, filed May 26, 2006 now U.S. Pat. No.7,235,981, which claims priority to Japanese Patent Application JP2005-174657 filed with the Japanese Patent Office on Jun. 15, 2005, theentire contents of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an impedance conversion circuit thatmakes an impedance including an inductance and an integrated circuitincluding thereof.

2. Description of the Related Art

It is difficult to make a desired impedance, especially an inductancewithin a semiconductor integrated circuit.

Japanese Patent Laid-open No. Hei 11-205087 discloses an impedanceconversion circuit using a plurality of operational amplifiers as shownin FIG. 25 as a circuit that makes an impedance including an inductance.

In this impedance conversion circuit, impedances Z1, Z2, Z3, Z4, and Z5are connected in series with each other between an input terminal 91,which is supplied with an input signal voltage Vin, and a ground. Theinput terminal 91 and a connection node of the impedances Z2 and Z3 areconnected to the non-inverting input terminal and the inverting inputterminal of an operational amplifier 92. The output terminal of theoperational amplifier 92 is connected to a connection node of theimpedances Z3 and Z4. A connection node of the impedances Z4 and Z5 anda connection node of the impedances Z2 and Z3 are connected to thenon-inverting input terminal and the inverting input terminal of anoperational amplifier 93. The output terminal of the operationalamplifier 93 is connected to a connection node of the impedances Z1 andZ2.

In the impedance conversion circuit, as shown in FIG. 25, an impedanceZin as viewed from the input terminal 91 isZin=(Z1·Z3·Z5)/(Z2·Z4)  (91)

SUMMARY OF THE INVENTION

However, the impedance conversion circuit in the related art shown inFIG. 25 is based on a precondition that the impedance is made betweenthe input terminal 91 and the ground. Thus, in order to extract theimpedance as a two-terminal element, a total of four operationalamplifiers are used. Further, in order to extract the impedance as afour-terminal element, a total of eight operational amplifiers are used.Thus, when converted to a two-terminal element or converted to afour-terminal element, the impedance invites an increase in powerconsumption, and is therefore not suitable for reduction of powerconsumption.

In addition, since the characteristic, especially the frequencycharacteristic of the created impedance is determined by the performanceof operational amplifiers being used, frequencies for use are limitedmore as the number of operational amplifiers is increased.

Accordingly, the present invention makes it possible to form animpedance conversion circuit with a small number of elements, reducepower consumption, and widen a frequency band for use.

According to an embodiment of the present invention, there is providedan impedance conversion circuit including: a first voltage-to-currentconverter and a second voltage-to-current converter supplied withdifferential input signal voltages; an inverting amplifier; and a thirdvoltage-to-current converter for feedback. In the impedance conversioncircuit, a first resistance and a second resistance are connected inseries with each other between an input terminal and an output terminalof the inverting amplifier, an output terminal of the firstvoltage-to-current converter is connected to the input terminal of theinverting amplifier, and an output terminal of the secondvoltage-to-current converter is connected to a connection node of thefirst resistance and the second resistance. Further, in the impedanceconversion circuit, the output terminal of the inverting amplifier isconnected to an input terminal of the third voltage-to-currentconverter, an output terminal of the third voltage-to-current converteris connected to an input terminal of the first voltage-to-currentconverter, and an impedance is connected between the connection node anda ground.

The thus formed impedance conversion circuit according to an embodimentof the present invention uses one inverting amplifier such as anoperational amplifier or the like, and the voltage-to-current converterscan be formed with a very small number of elements. Thus, even in thecase of conversion to a two-terminal element or conversion to afour-terminal element, it is possible to form an impedance conversioncircuit with a small number of elements, reduce power consumption, andwiden a frequency band for use.

As described above, according to an embodiment of the present invention,it is possible to form an impedance conversion circuit with a smallnumber of elements, reduce power consumption, and widen a frequency bandfor use.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an impedance conversion circuit according toa first embodiment;

FIG. 2 is a diagram showing an equivalent circuit of the circuit of FIG.1;

FIG. 3 is a diagram showing a band-pass filter formed by the circuit ofFIG. 1;

FIG. 4 is a diagram showing equations of assistance in explaining thecircuits of FIGS. 1 to 3;

FIG. 5 is a diagram showing an impedance conversion circuit according toa second embodiment;

FIG. 6 is a diagram showing an equivalent circuit of the circuit of FIG.5;

FIG. 7 is a diagram showing an equivalent circuit of the circuit of FIG.5;

FIG. 8 is a diagram showing a differential type band-pass filter formedby the circuit of FIG. 5;

FIG. 9 is a diagram showing equations of assistance in explaining thecircuits of FIGS. 5 to 8;

FIG. 10 is a diagram showing an impedance conversion circuit accordingto a third embodiment;

FIG. 11 is a diagram showing an equivalent circuit of the circuit ofFIG. 10;

FIG. 12 is a diagram showing an equivalent circuit of the circuit ofFIG. 10;

FIG. 13 is a diagram showing a symmetrical four-terminal network formedby the circuit of FIG. 10;

FIG. 14 is a diagram showing a differential type trap circuit formed bythe circuit of FIG. 10;

FIG. 15 is a diagram showing equations of assistance in explaining thecircuits of FIGS. 10 to 14;

FIG. 16 is a diagram showing equations of assistance in explaining thecircuits of FIGS. 10 to 14;

FIG. 17 is a diagram showing an impedance conversion circuit accordingto a fourth embodiment;

FIG. 18 is a diagram showing the circuit of FIG. 17 provided with driveresistances and terminating resistances;

FIG. 19 is a diagram showing a different representation of the circuitof FIG. 18;

FIG. 20 is a diagram showing a symmetrical four-terminal network formedby the circuit of FIG. 17;

FIG. 21 is a diagram showing a differential type third-order low-passfilter formed by the circuit of FIG. 17;

FIG. 22 is a diagram showing equations of assistance in explaining thecircuits of FIGS. 17 to 21;

FIG. 23 is a diagram showing equations of assistance in explaining thecircuits of FIGS. 17 to 21;

FIG. 24 is a diagram showing an impedance conversion circuit accordingto a fifth embodiment; and

FIG. 25 is a diagram showing an impedance conversion circuit in therelated art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 1. First Embodiment:FIGS. 1 to 4

FIG. 1 shows an impedance conversion circuit according to a firstembodiment.

The impedance conversion circuit in this example is formed as a circuit10 including voltage-to-current converters 11, 12, and 13 and aninverting amplifier 14.

The voltage-to-current converter 11 converts an input signal voltage Vinsupplied to an input terminal 1 a to an output current. Thevoltage-to-current converter 12 converts a differential (opposite phase)input signal voltage −Vin with respect to the input signal voltage Vin,the input signal voltage −Vin being supplied to an input terminal 1 b,to an output current.

An operational amplifier or the like can be used as the invertingamplifier 14. Resistances 15 and 16 are connected in series with eachother between the input terminal (an inverting input terminal in thecase of an operational amplifier) and the output terminal of theinverting amplifier 14. An impedance 18 is connected between aconnection node 17 of the resistances 15 and 16 and a ground. The outputterminal of the voltage-to-current converter 11 is connected to theinput terminal of the inverting amplifier 14. The output terminal of thevoltage-to-current converter 12 is connected to the connection node 17.

The voltage-to-current converter 13 converts an output voltage Vout ofthe inverting amplifier 14 to a current, and feeds back the current tothe input side of the voltage-to-current converter 11. That is, theinput terminal of the voltage-to-current converter 13 is connected tothe output terminal of the inverting amplifier 14. The output terminalof the voltage-to-current converter 13 is connected to the inputterminal of the voltage-to-current converter 11.

In the thus formed impedance conversion circuit, gm1, gm2, and gm0express the conductances (voltage-to-current conversion coefficients) ofthe voltage-to-current converters 11, 12, and 13, respectively. R1 andR2 express the resistance values of the resistances 15 and 16,respectively. Z expresses to be the impedance value of the impedance 18(for the impedance, an Arabic numeral is used as a reference numeral forthe meaning of a circuit or an element, and an alphabetical notation ofZ, Zin or the like is used for the meaning of an impedance value). Theoutput voltage Vout of the inverting amplifier 14 is expressed byEquation (1) in FIG. 4.

Supposing that a condition expressed by Equation (2) in FIG. 4 issatisfied between gm1 and gm2, the output voltage Vout is expressed byEquation (3) in FIG. 4.

Thus, a current Iin flowing from the voltage-to-current converter 13 tothe input side of the voltage-to-current converter 11 is expressed byEquation (4) in FIG. 4, and an impedance Zin as viewed from the inputterminal 1 a is expressed by Equation (5) in FIG. 4.

Letting Z=sL (where s is a Laplace operator), it is known in this casethat the input impedance Zin is an inductance. Varying gm0 can changethe value of the inductance, that is, the value of the impedance.

The parameter gm1, R1, or R2 other than gm0 can be changed. In thiscase, however, other parameters are changed in such a manner as to beinterlocked with the changing of the parameter gm1, R1, or R2 in orderto satisfy the condition of Equation (2) in FIG. 4. Thus, parameterchange and control becomes difficult, and therefore gm0 is changed.

FIG. 2 shows an equivalent circuit as viewed from the input terminal 1 aof the impedance conversion circuit in the example of FIG. 1. In thiscircuit, the impedance Zin expressed by Equation (5) in FIG. 4 existsbetween a signal source 2 and a ground.

FIG. 3 shows, as a concrete example, a band-pass filter 51 formed byusing a parallel connection circuit of an inductance and a capacitor asthe impedance 18 (impedance Z) in FIG. 1 with a drive resistance 3(resistance value R) attached.

With a configuration in which a linear element such as a resistance orthe like is used as the impedance 18 (impedance Z) and gm0 or gm1 can bechanged, it is possible to realize a gain control amplifier circuit witha linear gain control characteristic.

2. Second Embodiment: FIGS. 5 to 9

FIG. 5 shows an impedance conversion circuit according to a secondembodiment. The impedance conversion circuit in this example is formedby symmetrically disposing the circuit 10 shown in FIG. 1 and a circuit20 having the same configuration as that of the circuit 10 fordifferential input signal voltages Vin and −Vin.

Specifically, in the circuit 20, voltage-to-current converters 21, 22,and 23, an inverting amplifier 24, resistances 25 and 26, a connectionnode 27, and an impedance 28 are connected in exactly the same manner asin the circuit 10. In contrast to the circuit 10, the input signalvoltage −Vin given to an input terminal 1 b is supplied to thevoltage-to-current converter 21, and the input signal voltage Vin givento an input terminal 1 a is supplied to the voltage-to-current converter22.

Letting gm1 be the conductance of the voltage-to-current converters 11and 21, gm2 be the conductance of the voltage-to-current converters 12and 22, gm0 be the conductance of the voltage-to-current converters 13and 23, R1 be the resistance value of resistances 15 and 25, R2 be theresistance value of resistances 16 and 26, and Z be the impedance valueof the impedance 18 and 28, the output voltage Vout of the invertingamplifier 14 is expressed by Equation (11) in FIG. 9, which is the sameas Equation (1) in FIG. 4. The output voltage Vout′ of the invertingamplifier 24 is similarly expressed by Equation (12) in FIG. 9. Theoutput voltages Vout and Vout′ are in differential relation to eachother, as expressed by Equation (13) in FIG. 9.

Supposing that a condition expressed by Equation (14) in FIG. 9, whichis the same as Equation (2) in FIG. 4, is satisfied between gm1 and gm2,the output voltage Vout′ is expressed by Equation (15) in FIG. 9. G inEquation (15) is a transfer function expressed by Equation (16) in FIG.9.

Thus, a current Iin′ flowing from the voltage-to-current converter 23 tothe input side of the voltage-to-current converter 21 is expressed byEquation (17) in FIG. 9, and an impedance Zin′ as viewed from the inputterminal 1 b is expressed by Equation (18) in FIG. 9, which is the sameas Equation (5) in FIG. 4.

That is, in the example of FIG. 5, the impedance Zin as viewed from theinput terminal 1 a and the impedance Zin′ as viewed from the inputterminal 1 b are identical with each other, and appear between a groundand the input terminals 1 a and 1 b, respectively. This is equivalent tothe impedance Zin expressed by Equation (5) in FIG. 4 and the impedanceZin′ expressed by Equation (18) in FIG. 9 being connected in series witheach other between the input terminals 1 a and 1 b.

Hence, an equivalent circuit as viewed from the input terminals 1 a and1 b of the impedance conversion circuit in the example of FIG. 5 has twoidentical impedances Zin connected in series with each other between asignal source 2 a and a signal source 2 b, as shown in FIG. 6.

FIG. 7 shows an equivalent circuit when respective parts generating thetransfer function G expressed by Equation (16) in FIG. 9 in the circuits10 and 20 in FIG. 5 are shown as arithmetic circuits 5 a and 5 b.

FIG. 8 shows, as a concrete example, a differential type band-passfilter 52 formed by using a parallel connection circuit of an inductanceand a capacitor as the impedances 18 and 28 (impedance Z) in FIG. 5 withdrive resistances 3 a and 3 b (resistance value R) attached.

With a configuration in which a linear element such as a resistance orthe like is used as the impedances 18 and 28 (impedance Z) and gm0 orgm1 can be changed, it is possible to realize a gain control amplifiercircuit with a linear gain control characteristic.

3. Third Embodiment: FIGS. 10 to 16

FIG. 10 shows an impedance conversion circuit according to a thirdembodiment. The impedance conversion circuit in this example is formedby circuits 31 and 32.

In the circuit 31, two voltage-to-current converters 11 a and 11 b areprovided as converters corresponding to the voltage-to-current converter11 in the impedance conversion circuit in the example of FIG. 5, twovoltage-to-current converters 12 a and 12 b are provided as converterscorresponding to the voltage-to-current converter 12, and twovoltage-to-current converters 13 a and 13 b are provided as converterscorresponding to the voltage-to-current converter 13. Resistances 15 and16 are connected in series with each other between the input terminaland the output terminal of an inverting amplifier 14. An impedance 18 isconnected between a connection node 17 of the resistances 15 and 16 anda ground. The output terminals of the voltage-to-current converters 11 aand 11 b are connected to the input terminal of the inverting amplifier14. The output terminals of the voltage-to-current converters 12 a and12 b are connected to the connection node 17. The input terminals of thevoltage-to-current converters 13 a and 13 b are connected to the outputterminal of the inverting amplifier 14. The output terminal of thevoltage-to-current converter 13 a is connected to the input terminal ofthe voltage-to-current converter 11 a. The output terminal of thevoltage-to-current converter 13 b is connected to the input terminal ofthe voltage-to-current converter 11 b.

In the circuit 32, two voltage-to-current converters 21 a and 21 b areprovided as converters corresponding to the voltage-to-current converter21 in the impedance conversion circuit in the example of FIG. 5, twovoltage-to-current converters 22 a and 22 b are provided as converterscorresponding to the voltage-to-current converter 22, and twovoltage-to-current converters 23 a and 23 b are provided as converterscorresponding to the voltage-to-current converter 23. Resistances 25 and26 are connected in series with each other between the input terminaland the output terminal of an inverting amplifier 24. An impedance 28 isconnected between a connection node 27 of the resistances 25 and 26 andthe ground. The output terminals of the voltage-to-current converters 21a and 21 b are connected to the input terminal of the invertingamplifier 24. The output terminals of the voltage-to-current converters22 a and 22 b are connected to the connection node 27. The inputterminals of the voltage-to-current converters 23 a and 23 b areconnected to the output terminal of the inverting amplifier 24. Theoutput terminal of the voltage-to-current converter 23 a is connected tothe input terminal of the voltage-to-current converter 21 a. The outputterminal of the voltage-to-current converter 23 b is connected to theinput terminal of the voltage-to-current converter 21 b.

Further, in the circuits 31 and 32, the input terminals of thevoltage-to-current converters 11 a and 22 a and the output terminal ofthe voltage-to-current converter 13 a are connected as a terminal 1 a.The input terminals of the voltage-to-current converters 12 a and 21 aand the output terminal of the voltage-to-current converter 23 a areconnected as a terminal 1 b. The input terminals of thevoltage-to-current converters 11 b and 22 b and the output terminal ofthe voltage-to-current converter 13 b are connected as a terminal 1 d.The input terminals of the voltage-to-current converters 12 b and 21 band the output terminal of the voltage-to-current converter 23 b areconnected as a terminal 1 c. The terminals 1 a and 1 b are provided withdifferential input signal voltages Va and Vb.

Also in this example, supposing that a condition expressed by Equation(14) in FIG. 9 is satisfied, and letting Vc and Vd be the voltages ofthe terminals 1 c and 1 d, respectively, in this example, the outputvoltage Vout of the inverting amplifier 14 and the output voltage Vout′of the inverting amplifier 24 are expressed by Equation (21) andEquation (22) in FIG. 15, with Equation (14) substituted into Equation(11) and Equation (12) in FIG. 9, expressed Vin=Va−Vd in Equation (11),and −Vin=Vb−Vc in Equation (12).

G in Equation (21) and Equation (22) is a transfer function expressed byEquation (23) in FIG. 15, which is the same as Equation (16) in FIG. 9.

Hence, an equivalent circuit of the impedance conversion circuit in theexample of FIG. 10 can be represented as shown in FIG. 11 when partsgenerating the transfer function G expressed by Equation (23) in FIG. 15are shown as arithmetic circuits 6 a and 6 b, respectively.

FIG. 12 shows a state of the equivalent circuit in which driveresistances 3 a and 3 b (resistance value R) and terminating resistances4 c and 4 d (resistance value R) are further added. Signal sources 2 aand 2 b provide differential input signal voltages Vin and −Vin.

In the circuit of FIG. 12, letting Ia be a current flowing through thedrive resistance 3 a and Id be a current flowing through the terminatingresistance 4 d, Equation (31) and Equation (32) in FIG. 15 hold for thecurrents Ia and Id. The voltage Vd is expressed by Equation (33) in FIG.15. Hence, the voltages Va and Vd are expressed by Equation (34) andEquation (35) in FIG. 15.

Similarly, letting Ib be a current flowing through the drive resistance3 b and Ic be a current flowing through the terminating resistance 4 c,Equation (41) and Equation (42) in FIG. 15 hold for the currents Ib andIc. The voltage Vc is expressed by Equation (43) in FIG. 15. Hence, thevoltages Vb and Vc are expressed by Equation (44) and Equation (45) inFIG. 15.

As is clear from a comparison between Equation (34) and Equation (44)and a comparison between Equation (35) and Equation (45), the voltage Vaand the voltage Vb are in differential relation to each other, and thevoltage Vd and the voltage Vc are in differential relation to eachother.

Further, from Equation (34) in FIG. 15, the current Ia is expressed byEquation (51) in FIG. 16. From Equation (44) in FIG. 15, the current Ibis expressed by Equation (52) in FIG. 16. From Equation (35) in FIG. 15,the current Id is expressed by Equation (53) in FIG. 16. From Equation(45) in FIG. 15, the current Ic is expressed by Equation (54) in FIG.16.

It is understood from Equations (51) to (54) that the currents Ia, Ib,Id, and Ic all have an equal absolute value, that the current Ia flowsin a direction of an arrow in FIG. 12 from the terminal 1 a to theterminal 1 d, and that the current Ib flows in an opposite direction ofan arrow in FIG. 12 from the terminal 1 c to the terminal 1 b.

That is, the impedance conversion circuit in the example of FIG. 10forms a symmetrical four-terminal network 30 with two input terminalsand two output terminals, as shown in FIG. 13.

Voltages V1 and −V1 in FIG. 13 correspond to the voltages Va and Vbexpressed by Equation (34) and Equation (44) in FIG. 15 and indicatethat the two voltages are in differential relation to each other.Voltages V2 and −V2 in FIG. 13 correspond to the voltages Vc and Vdexpressed by Equation (45) and Equation (35) in FIG. 15 and indicatethat the two voltages are in differential relation to each other.

From Equation (34) and Equation (44) in FIG. 15, the voltage V1 isexpressed by Equation (55) in FIG. 16. From Equation (45) and Equation(35) in FIG. 15, the voltage V2 is expressed by Equation (56) in FIG.16. Letting Z12 be an impedance between the terminals 1 a and 1 d,Equation (57) in FIG. 16 holds, and the impedance Z12 is expressed byEquation (58) in FIG. 16. An impedance between the terminals 1 b and 1 cis the same impedance Z12.

Thus, the impedance conversion circuit in the example of FIG. 10 formsthe symmetrical four-terminal network 30 between the terminals 1 a, 1 b,1 d, and 1 c.

What is important is that in the case of the differential inputs on aninput side and the differential outputs on an output side in thefour-terminal network, an impedance as expressed by Equation (58) inFIG. 16 exists as a two-terminal element between the inputs and theoutputs in the symmetrical four-terminal network, and that at the sametime, various four-terminal networks can be made by a configuration ofthe used impedance Z. In addition, in the above-described example, it ispossible to change the created impedance Z12 by varying gm0.

FIG. 14 shows, as a concrete example, a differential type (second-ordersymmetrical four-terminal type in this case) trap circuit 53 formed byusing a parallel connection circuit of an inductance and a capacitor asthe impedances 18 and 28 (impedance Z) in FIG. 10.

As in the impedance conversion circuit in the example of FIG. 5, with aconfiguration in which a linear element such as a resistance or the likeis used as the impedances 18 and 28 (impedance Z) and gm0 or gm1 can bechanged, it is possible to realize a gain control amplifier circuit witha linear gain control characteristic.

4. Fourth Embodiment: FIGS. 17 to 23

FIG. 17 shows an impedance conversion circuit according to a fourthembodiment.

The impedance conversion circuit in this case is formed by providing theimpedance conversion circuit in the example of FIG. 10 forming asymmetrical four-terminal network as in FIG. 11 (FIG. 13) as anequivalent circuit with impedances 7 a and 7 b (impedance Z11) as abridge between the terminals 1 a and 1 b on the input side andimpedances 7 c and 7 d (impedance Z22) as a bridge between the terminals1 c and 1 d on the output side.

Also in this case, supposing that a condition expressed by Equation (14)in FIG. 9 is satisfied, the output voltage Vout of an arithmetic circuit6 a is expressed by Equation (61) in FIG. 22, which is the same asEquation (21) in FIG. 15. G in Equation (61) is a transfer functionexpressed by Equation (62) in FIG. 22, which is the same as Equation(23) in FIG. 15.

In this case, as shown in Equation (63) in FIG. 22, G is replaced withG12, and gm0 is replaced with gm12.

Thus, as shown in FIG. 17, the transfer function generated by arithmeticcircuits 6 a and 6 b is G12, and the conductance of voltage-to-currentconverters 13 a, 13 b, 23 a, and 23 b is gm12.

FIG. 18 shows a state in which drive resistances 3 a and 3 b (resistancevalue R) and terminating resistances 4 c and 4 d (resistance value R)are further added. As described above with reference to FIG. 12, signalsources 2 a and 2 b provide differential input signal voltages Vin and−Vin.

In the circuit of FIG. 18, currents Ia and Ib flowing through the driveresistances 3 a and 3 b are expressed by Equation (65) and Equation (66)in FIG. 22, and currents Ic and Id flowing through the terminatingresistances 4 c and 4 d are expressed by Equation (67) and Equation (68)in FIG. 22.

Subtracting Equation (68) from Equation (65) and subtracting Equation(67) from Equation (66) gives voltages Vc and Vd expressed by Equation(71) and Equation (72) in FIG. 23. Further, adding Equation (71) andEquation (72) provides a sum of the voltage Vc and the voltage Vd asexpressed by Equation (73) in FIG. 23. In addition, adding Equation (65)and Equation (66) in FIG. 22 provides a sum of the voltage Vc and thevoltage Vd as expressed by Equation (74) in FIG. 23.

Thus, since Equation (73) is equal to Equation (74), as shown byEquation (75) in FIG. 23, a sum of a voltage Va and a voltage Vb and asum of the voltage Vc and the voltage Vd are each zero, and as shown byEquation (76) in FIG. 23, the voltage Va and the voltage Vb are indifferential relation to each other and the voltage Vc and the voltageVd are in differential relation to each other. Further, it is understoodfrom these differential relations that as for the currents expressed byEquations (65) to (68) in FIG. 22, Ib=Ia and Id=−Ic.

From the above results, the circuit of FIG. 18 can be represented as inFIG. 19. Voltages V1 and −V1 in FIG. 19 correspond to the voltages Vaand Vb and indicate that the two voltages are in differential relationto each other. Voltages V2 and −V2 correspond to the voltages Vc and Vdand indicate that the two voltages are in differential relation to eachother.

One impedance 7 e represents the impedances 7 a and 7 b on the inputside. One impedance 7 f represents the impedances 7 c and 7 d on theoutput side.

As described above with reference to FIGS. 10 to 14, in the case of thedifferential inputs on the input side and the differential outputs onthe output side in the four-terminal network, an impedance Z12 expressedby Equation (58) in FIG. 16 exists as a two-terminal element between theinputs and the outputs.

Also in the example of FIGS. 17 to 19, as shown in FIG. 20, an impedanceZ12 expressed by Equation (78) in FIG. 23, which equation is obtained byrewriting Equation (58) in FIG. 16, exists as a two-terminal element.

Thus, in this example, a ladder circuit can be formed as shown in FIG.20. It is thereby possible to realize a steep filtering characteristicof a Chebyshev filter or the like within an integrated circuit.

FIG. 21 shows, as a concrete example, a differential type third-orderlow-pass filter (third-order Chebyshev type low-pass filter) 54 formedby using a parallel connection circuit of an inductance and a capacitoras the impedance Z (impedances 18 and 28 that, though not shown in FIG.17, are shown in FIG. 10) and using a capacitor as the impedances 7 eand 7 f.

As in the impedance conversion circuit in the example of FIG. 10, with aconfiguration in which a linear element such as a resistance or the likeis used as the impedances 18 and 28 (impedance Z) and gm12 or gm1 can bechanged, it is possible to realize a gain control amplifier circuit witha linear gain control characteristic.

5. Fifth Embodiment: FIG. 24

FIG. 24 shows an impedance conversion circuit according to a fifthembodiment.

This example is basically the same as the example of FIG. 17. In thiscase, an impedance between terminals 1 a and 1 b on an input side is setas the above-described impedance Z11, and the impedance Z11 is formed asa differential type impedance by an arithmetic circuit 41 andvoltage-to-current converters 42 and 43. An impedance between terminals1 c and 1 d on an output side is set as the above-described impedanceZ22, and the impedance Z22 is formed as a differential type impedance byan arithmetic circuit 45 and voltage-to-current converters 46 and 47.

Suppose that the arithmetic circuit 41 generates a transfer functionG11, and that the arithmetic circuit 45 generates a transfer functionG22. Suppose that the conductance of the voltage-to-current converters42 and 43 is gm11, and that the conductance of the voltage-to-currentconverters 46 and 47 is gm22.

In this case, the impedances Z11 and Z22 and an impedance Z12 betweenthe terminals 1 a and 1 d and between the terminals 1 b and 1 c areexpressed by:Z11=2×G11×gm11  (81)Z22=2×G22×gm22  (82)Z12=G12×gm12  (83)

Also in this example, as in the example of FIG. 17, a ladder circuit asshown in FIG. 20 can be formed, and a differential type third-orderlow-pass filter (third-order Chebyshev type low-pass filter) as shown inFIG. 21 can be formed.

6. Effects of Embodiments

The impedance conversion circuit according to each of theabove-described embodiments can be formed by a smaller number ofelements than the impedance conversion circuit in the related art. It istherefore possible to reduce power consumption, widen a frequency bandfor use, and realize an active filter for up to a high frequency.

By using an operational amplifier having a wide dynamic range as aninverting amplifier, it is possible to widen the dynamic ranges of inputand output, and filter a massive input.

The use of voltage-to-current converters in an input part enables allbias points to be set at a center of power supply voltage, which isadvantageous in decreasing voltage and increases resistance todistortion. In addition, a CMOS process unsuitable for active filters inthe past can be used.

Because a symmetrical four-terminal network can be formed by a smallernumber of elements than that of the related art, it is possible to widena frequency band for use, realize an active filter for up to a highfrequency, and realize a steep filtering characteristic.

It is possible to freely control an impedance value after conversion bya ratio between the conductance of a voltage-to-current converter and aresistance value for the impedance value being used, and thus easilyrealize an impedance having an appropriate value within an integratedcircuit.

The formation of a symmetrical four-terminal network enablesdifferential processing of all signals, and thus enables analog signalprocessing highly resistant to noise such as radiation or the likewithin the integrated circuit.

With a configuration in which a linear element such as a resistance orthe like is used as impedance Z and the conductance of avoltage-to-current converter can be changed, it is possible to realize again control amplifier circuit with a linear gain controlcharacteristic.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A signal processing method using an impedance conversion circuitcomprising: providing a first voltage-to-current converter and a secondvoltage-to-current converter supplied with differential input signalvoltages; providing an inverting amplifier; and generating a feedbacksignal with a third voltage-to-current converter, wherein a firstresistance and a second resistance are connected in series with eachother between an input terminal and an output terminal of said invertingamplifier, an output terminal of said first voltage-to-current converteris connected to the input terminal of said inverting amplifier, anoutput terminal of said second voltage-to-current converter is connectedto a connection node of said first resistance and said secondresistance, the output terminal of said inverting amplifier is connectedto an input terminal of said third voltage-to-current converter, anoutput terminal of said third voltage-to-current converter is connectedto an input terminal of said first voltage-to-current converter, and animpedance is connected between said connection node and a ground.
 2. Asignal processing method using an impedance conversion circuitcomprising: providing a first circuit and a second circuit; wherein eachof the two circuits includes a first voltage-to-current converter and asecond voltage-to-current converter, an inverting amplifier, and a thirdvoltage-to-current converter for feedback; providing a first resistanceand a second resistance connected in series with each other between aninput terminal and an output terminal of said inverting amplifier;wherein an output terminal of said first voltage-to-current converter isconnected to the input terminal of said inverting amplifier; an outputterminal of said second voltage-to-current converter connected to aconnection node of said first resistance and said second resistance; theoutput terminal of said inverting amplifier connected to an inputterminal of said third voltage-to-current converter; an output terminalof said third voltage-to-current converter being connected to an inputterminal of said first voltage-to-current converter; and an impedancebeing connected between said connection node and a ground, supplying anidentical input signal voltage to said first voltage-to-currentconverter in said first circuit and said second voltage-to-currentconverter in said second circuits and supplying a differential inputsignal voltage with respect to said input signal voltage to said firstvoltage-to-current converter in said second circuit and said secondvoltage-to-current converter in said first circuit.
 3. A signalprocessing method using impedance conversion circuit comprising:providing a first circuit and a second circuit; wherein each of the twocircuits includes a first voltage-to-current converter, a secondvoltage-to-current converter, a third voltage-to-current converter, afourth voltage-to-current converter, a fifth voltage-to-currentconverter, and a sixth voltage-to-current converter, and an invertingamplifier; providing a first resistance and a second resistanceconnected in series with each other between an input terminal and anoutput terminal of said inverting amplifier; wherein an output terminalof said first voltage-to-current converter and an output terminal ofsaid fourth voltage-to-current converter is connected to the inputterminal of said inverting amplifier; an output terminal of said secondvoltage-to-current converter and an output terminal of said fifthvoltage-to-current converter is connected to a connection node of saidfirst resistance and said second resistance; the output terminal of saidinverting amplifier being connected to an input terminal of said thirdvoltage-to-current converter and an input terminal of said sixthvoltage-to-current converter; an output terminal of said thirdvoltage-to-current converter being connected to an input terminal ofsaid first voltage-to-current converter; an output terminal of saidsixth voltage-to-current converter being connected to an input terminalof said fourth voltage-to-current converter; and an impedance beingconnected between said connection node and a ground, wherein the inputterminal of said first voltage-to-current converter in said firstcircuit and the input terminal of said second voltage-to-currentconverter in said second circuit are connected as a first terminal, theinput terminal of said first voltage-to-current converter in said secondcircuit and the input terminal of said second voltage-to-currentconverter in said first circuit are connected as a second terminal, theinput terminal of said fourth voltage-to-current converter in said firstcircuit and the input terminal of said fifth voltage-to-currentconverter in said second circuit are connected as a third terminal, theinput terminal of said fourth voltage-to-current converter in saidsecond circuit and the input terminal of said fifth voltage-to-currentconverter in said first circuit are connected as a fourth terminal, andsaid first terminal and second terminal are supplied with differentialinput signal voltages.
 4. The signal processing method using animpedance conversion circuit as claimed in claim 3, wherein an impedanceis connected between said first terminal and said second terminal, andan impedance is connected between said third terminal and said fourthterminal.
 5. The signal processing method using an impedance conversioncircuit as claimed in claim 4, wherein said impedances are differentialtype impedances.
 6. A method of manufacturing an integrated circuitcomprising: providing a first voltage-to-current converter and a secondvoltage-to-current converter which are to be supplied with differentialinput signal voltages; providing an inverting amplifier; and a thirdvoltage-to-current converter for feedback, wherein a first resistanceand a second resistance are connected in series with each other betweenan input terminal and an output terminal of said inverting amplifier,wherein an output terminal of said first voltage-to-current converter isconnected to the input terminal of said inverting amplifier, an outputterminal of said second voltage-to-current converter is connected to aconnection node of said first resistance and said second resistance, theoutput terminal of said inverting amplifier is connected to an inputterminal of said third voltage-to-current converter, an output terminalof said third voltage-to-current converter is connected to an inputterminal of said first voltage-to-current converter, and an impedance isconnected between said connection node and a ground.